Profiles of mathematical deficits in children with dyslexia

Dyslexia, a neurodevelopmental disorder affecting accurate and fluent word recognition, impacts approximately 5-10% of the global population. While primarily associated with reading difficulties, a significant comorbidity exists with mathematical difficulties, with prevalence estimates ranging from 20% to 70%. This high rate of overlap highlights the need for a better understanding of the specific mathematical deficits experienced by children with dyslexia. Existing research suggests that these difficulties are not limited to number processing but can involve various aspects of mathematical cognition, including arithmetic fact retrieval and calculation abilities. The lack of comprehensive studies examining the various components of mathematical skills in children with dyslexia motivated the development and evaluation of a new assessment tool: the UCSF Mathematical Cognition Battery (MCB). The MCB aims to identify deficits in four distinct mathematical domains: 1. number processing; 2. arithmetical procedures; 3. arithmetic facts retrieval; and 4. geometrical abilities. This study utilizes the MCB to characterize the profiles of mathematical deficits in a large cohort of children diagnosed with dyslexia, furthering our understanding of the complex relationship between linguistic and mathematical abilities and paving the way for more effective and targeted interventions.

A considerable body of research indicates a strong association between dyslexia and mathematical difficulties. Studies report that a substantial proportion (around 40%) of children with reading difficulties also struggle with mathematics. Prevalence rates for the overlap between dyslexia and dyscalculia vary widely (17-64%), emphasizing the heterogeneity of mathematical challenges in this population. Mathematical difficulties in dyslexic children aren't solely restricted to number processing; difficulties in arithmetic fact retrieval from long-term memory are also frequently observed. Furthermore, impairments in cognitive domains such as verbal and visuospatial working memory, and lexical naming speed have been linked to the co-occurrence of reading and mathematical challenges. The existing literature highlights the need for a more nuanced understanding of the specific mathematical profiles present in dyslexia, which is critical for developing effective interventions. Current standardized assessments may not adequately capture the diverse nature of these mathematical challenges, thus motivating the creation of the UCSF MCB.

The UCSF Mathematical Cognition Battery (MCB) was developed based on cognitive neuroscience research, focusing on four core domains of mathematical cognition: number processing, arithmetical procedures, arithmetic facts retrieval, and geometrical abilities. The battery comprises 19 subtests—four computer-based and fifteen paper-based—tailored for children in grades 2 through 8. Number processing subtests assess skills in manipulating, generating, and interpreting numbers across various formats (digits, words, pictures). Arithmetical procedures subtests evaluate mental and written calculation skills, encompassing addition, subtraction, multiplication, and division. Arithmetic facts retrieval is assessed through tests of memorization and recall of basic arithmetic facts. Geometrical abilities are evaluated via tasks involving shape recognition, spatial reasoning, and geometrical transformations. The study included 75 children diagnosed with dyslexia at the UCSF Dyslexia Center and 18 typically developing controls, aged 7 to 16. A team of clinicians classified the dyslexic children into subgroups based on reported symptoms and clinical history: those without mathematical deficits and those with deficits in each of the four mathematical domains. The MCB was then administered to confirm these clinical impressions. Neuropsychological and academic standardized tests were also administered to assess broader cognitive abilities. Statistical analyses, including ANOVA and t-tests, were used to compare performance across groups, accounting for multiple comparisons using the Bonferroni correction.

The study revealed a high prevalence of mathematical deficits among children with dyslexia: 66% (50 out of 75) of the dyslexic children exhibited such deficits. The UCSF MCB effectively confirmed the clinicians' initial classifications for the majority of the children, demonstrating its potential as a diagnostic tool. The results indicated heterogeneity in the types of mathematical deficits observed. A smaller percentage (13.3%) showed impairments in number processing, characterized by difficulties in understanding numerical magnitude and manipulating quantities. A larger percentage (40%) displayed deficits in either arithmetical procedures (20%) or arithmetic facts retrieval (20%), reflecting challenges in calculation or memorizing arithmetic facts, respectively. A smaller group (9.3%) exhibited deficits in geometrical abilities, reflecting difficulties in visuospatial processing and spatial reasoning. Three participants (4%) showed overlapping deficits and could not be classified into a specific subgroup. The study also observed that some children classified as having no mathematical difficulties based on standard assessments still showed subtle deficits on certain MCB subtests, suggesting a need for more comprehensive assessments. Furthermore, group differences were noted in neuropsychological tests, particularly for children with number processing deficits, showing lower performance in nonverbal reasoning, visuospatial skills, and calculation abilities. The typically developing children outperformed all other groups in Approximate Number System (ANS) tasks involving digits and, to a lesser extent, dots.

This study demonstrates the significant prevalence of mathematical deficits in children with dyslexia (66%), often undetected by standard assessments. The heterogeneity of these deficits highlights the limitations of using general mathematical assessments and underlines the need for more targeted approaches. The UCSF MCB, with its focus on distinct mathematical domains, successfully identified these diverse profiles, validating its potential as a clinical tool for improved diagnostic accuracy. The findings also suggest potential neurocognitive correlates associated with different mathematical deficit types, such as the link between number processing deficits and difficulties in visuospatial reasoning. The identification of distinct subtypes of mathematical difficulties in children with dyslexia opens up opportunities for the development of tailored interventions. Future research could explore the specific neurocognitive mechanisms underlying these subtypes and develop targeted interventions tailored to specific needs. The development of personalized educational approaches and interventions based on these distinct profiles could significantly improve the learning outcomes for children with dyslexia.

This study demonstrates the high prevalence and diverse nature of mathematical deficits in children with dyslexia. The UCSF MCB proved to be an effective tool for identifying and classifying these deficits into four distinct subgroups: number processing, arithmetical procedures, arithmetic facts retrieval, and geometrical abilities. These findings highlight the need for more comprehensive assessment tools and tailored interventions to address the specific mathematical needs of dyslexic children. Future research should focus on refining the MCB through standardization, increasing sample sizes, and further exploring the neurocognitive underpinnings of these distinct mathematical deficit profiles.

The relatively small sample size and unequal distribution across subgroups limit the statistical power of some analyses. The study relies on a clinical classification of mathematical deficits, which might introduce some subjectivity. While the UCSF MCB showed promise, further standardization and validation are needed before widespread clinical use. The study's focus on children with dyslexia might limit the generalizability of the findings to other populations with mathematical difficulties.